1. Field of the Invention
The present invention relates to a vehicle-information sharing system that allows electronic apparatuses having a vehicle-information determining function to share the same vehicle information.
2. Description of the Related Art
Electronic apparatuses installed in automobiles, such as TV sets, navigation systems, audio apparatuses, and audio control units, sometimes function on a standalone basis and sometimes operate according to the state of the vehicle. For example, the display of moving pictures on a TV screen may be prevented during driving for safety, and the backlight for the instrumental panel is brightened when it becomes dark, or conversely, is dimmed when it becomes light. In order to obtain vehicle information that indicates such a state of the vehicle, each electronic apparatus is connected to a supply source for vehicle information. For example, the electronic apparatus is connected to a parking brake (side brake) to determine whether the vehicle is running, and is connected to a dimmer switch (light switch) to judge the ambient brightness.
An electronic apparatus that needs vehicle information has an input line or input terminal through which vehicle information is input. FIG. 5 is an explanatory view showing the connection between electronic apparatuses and supply sources for vehicle information. Electronic apparatuses, namely, a navigation system 100, a TV set 110, an audio control unit 120, and an audio apparatus 130, respectively have input lines 140, 141, 142, and 143 for vehicle information. The input lines 140 to 143 are connected to a dimmer switch 150 and a parking bake 160, so that each electronic apparatus can determine whether the vehicle is running and whether it is dark.
Japanese Unexamined Patent Application Publication No. 9-27163 discloses an example of an electronic apparatus that acquires vehicle information. In this publication, a compact video disc player (master unit) and a cassette deck (master unit) are connected to a car-mounted disk changer through bus lines. When a detection circuit detects that the automobile is running, the compact video disc player is prevented from playing back moving pictures.
Japanese Unexamined Patent Application Publication No. 6-262984 discloses a technique for detecting whether the automobile is running, and preventing the display on a TV screen during driving while permitting a navigation system to display map information even during driving.
However, the known systems for acquiring vehicle information have the following problems. As shown in FIG. 5, it is troublesome and difficult to connect the input lines of all the electronic apparatuses that need vehicle information to the supply sources of vehicle information. In particular, when multiple electronic apparatuses are used, they are installed at different positions, for example, in the trunk, under the seat, and in the dashboard. While it is easy to connect a line, for example, from the lower side of the seat to the parking brake, it is quite troublesome to route a line thereto from the interior of the trunk over a long distance.
In contrast, when vehicle information from an input line is simply transmitted to other electronic apparatuses through a control bus, incorrect information is obtained from an input line that is not connected to the supply source for vehicle information. When the incorrect information is transmitted to the other electronic apparatuses, it is combined with correct information, and the correct information cannot be precisely ascertained. In order to solve this problem, the user may determine the connection of an input line of each electronic apparatus to the information supply source. For example, when the user makes a setting so that the audio control unit is connected to the supply source, but other apparatuses are not connected thereto, only vehicle information from the audio control unit is accepted and transmitted to the control bus, and vehicle information from the other apparatuses is not accepted and not transmitted to the control bus. In this case, the user must determine whether each electronic apparatus is enabled or disabled. This operation is troublesome, and erroneous settings by the user cannot be completely prevented.